The acetabulum is a part of the pelvis that comprises a substantially hemispherical cavity for receiving the femoral head which has a corresponding substantially spherical shape to form the hip joint.
The substantially hemispherical cavity of the acetabulum is bounded by the acetabular rim, which has a 3D contour.
In some cases, the acetabulum may suffer from a deformity that generated either over-coverage or under-coverage of the acetabulum with respect to the substantially hemispherical cavity.
An over-covered acetabulum causes a pincer lesion femoro-acetabular impingement (FAI) that limits the range of motion of the hip joint and leads to a conflict between the acetabulum and the femur.
To the contrary, an under-covered acetabulum causes hip dysplasia that leads to a lack of stability of the hip joint.
Surgical intervention for treatment of acetabular under-coverage (i.e. hip dysplasia) and over-coverage (i.e. pincer lesion in femoro-acetabular impingement (FAI)) has become an increasingly common procedure in the field of orthopaedic surgery.
In particular, a pincer lesion can be treated by resecting a part of the acetabulum in the region of the rim where over-coverage has been detected using either an arthroscopic or open surgical approach.
Hip dysplasia is often treated surgically with a peri-acetabular osteotomy (PAO) or total hip arthroplasty.
However, the current diagnostic methods for assessing acetabular coverage are primarily based on conventional 2D X-ray projection imaging or single CT/MRI slices and fail to appreciate the 3D nature of the acetabular deformity.
The most common X-ray measure of acetabular coverage is the lateral center-edge angle (CE angle), which only measures acetabular coverage at one location along the rim R, i.e. the most lateral point, as shown on FIG. 1A.
The cross-over sign is also used to identify cases of anterior over-coverage.
FIG. 1B illustrates an example of the measurement of the cross-over sign CO on a 2D X-ray image of the acetabulum.
However, the cross-over sign only provides a qualitative description of the anterior rim relative to the posterior rim.
In addition, various other measures, such as acetabular version, have been used in view of the assessment of the acetabular morphology, but they fail to provide an objective method of determining 3D pathologic coverage around the entire extent of the acetabulum.
Another method that has been used to assess acetabular coverage is based on 3D renderings generated from 3D medical images such as CT or MRI medical images.
Such a method is based on segmentation of the images to create 3D surface models of the acetabular morphology.
The surgeon can then perform a qualitative visual assessment of the acetabular coverage in order to determine whether surgery is appropriate and, if so, approximately define how much and where to resect the acetabular rim in the case of pincer FAI.
However, this method of visual acetabular coverage assessment is highly subjective, dependent on the surgeon's experience and interpretation of the 3D images.
Hence, there is currently no way for surgeons to assess the 3D acetabular morphology and to create a patient-specific pre-surgical plan that is capable of precisely identifying both the extent and the amount of bone to correct along the acetabular rim.
Thus, many patients receive an unnecessary, insufficient or over-aggressive surgical treatment of their acetabular pathology as a direct result of inadequate pre-operative 3D acetabular morphology assessment techniques.
Similar problems may arise in bones which have, like the acetabulum, a substantially hemispherical cavity bounded by a rim, e.g. the glenoid of the shoulder.
A goal of the invention is thus to overcome the above-mentioned problems and to provide a method for creating a surgical resection plan for treating a pathologic deformity of a bone having a rim bounding a substantially spherical cavity.